Although latent variable modeling is a branch of multivariate statistics, many of the field's major developments originated and were motivated by research problems, not within statistics, but rather from the psychological and social sciences [1]}. Whereas the early breakthroughs mainly came from psychology, educational measurement, and economics, the more recent advances are increasingly coming from the field of machine learning, especially from the very active research area of unsupervised learning in which researchers are trying to accomplish the goal of endowing computers the ability to learn complex data patterns in an unsupervised automatic manner [2]}, [3]}.
